Copending application Ser. No. 06/927629, filed Nov. 5, 1986, now U.S. Pat. No. 4,817,140, the disclosure of which is incorporated by this reference, describes a software copy protection mechanism which is unique in that it segregates the right to execute a particular piece of application software from a copy of the software itself. The software is protected to the extent that it is distributed in encrypted form. The protected software is executable on a composite computing system including a conventional host (which may be a mainframe computer although typically it would be represented by a PC) in combination with a physically and logically secure coprocessor. The logically and physically secure coprocessor basically performs two essential functions. The coprocessor stores a software decryption key (AK) for a protected application in secure, non-volatile storage; the software decryption key (AK) when installed in a coprocessor represents the, user's right to execute the protected application. The coprocessor also effects the decryption and execution of the protected application, and thus while it provides to the host the results of execution of the protected application, the protected application itself is maintained secure.
Typically, the protected application will be represented on a distribution media in at least two files, a first file of plain text software, which (to the extent it is present) is executed on the host, and a second file of encrypted software which will be executed on the coprocessor. The coprocessor, since it has access to the software decryption key, can read the software portion provided in encrypted form, and decrypt it so that its random access memory stores the protected software in plain text form. The physical and logical security provided by the coprocessor prevents the user (or a pirate) from obtaining access to clear text of the protected application. The coprocessor executes the protected application, passing only results onto the host. In this fashion, the entire application is executed but the user never has access to the protected application in plain text or executable form.
The present invention is directed at a simple, low cost implementation of the coprocessor, with respect to its logical security.
Processors exhibiting multiple privilege levels have been known in the prior art. With the introduction of multi-processing, the mainframe computer field found a need for implementing privilege structure at least to ensure that user #1's program and/or data did not interfere with or be interfered by user #2's program or data. In many cases the privilege structure was implemented in software. In the past, in the mainframe computing field, the software privilege structure was feasible because the system programmers and system operators were part and parcel of the security system and they would ensure that application programs complied with the necessary privilege structure.
There are processors which provide multi-level privilege structures, but those are too costly for use in such low cost applications as the present invention is directed at. The function of the privilege structure in prior art systems has been the separation of execution spaces of multiple users to insure meaningful, orderly, non-destructive use and allocation of system processing resources but not for copy protection of software. These do not always exhibit open architecture.
For the software asset protection mechanism described in application Ser. No. 927629, now U.S. Pat. No. 4,817,140 to be widely applied, the architecture of the coprocessor must be open to allow widespread use; this necessarily requires that the coprocessor and its instruction set will be widely known. Without some form of privilege structure, an application program could be written which would access information violating the security requirements, such as decryption keys, or the plain text version of protected software.
More particularly, as described in application Ser. No. 927629, now U.S. Pat. No. 4,817,140, the coprocessor must provide functions and data which are not available to the user. These include data encryption and decryption, the right to execute a specific application, and encryption keys. The coprocessor, in addition to implementing security, must also be capable of general purpose computing tasks since the protected portion of any application is intended to be executed on the coprocessor.
Accordingly, it is an object of the invention to provide, in accordance with a software asset protection mechanism, logical security for a coprocessor, which coprocessor is capable of general computing tasks. It is another object of the invention to provide logical security for such a coprocessor notwithstanding the fact that the internal architecture and instruction set for the coprocessor are expected to be widely circulated and known. It is another object of the present invention to provide a coprocessor for such a software asset protection mechanism which is capable of storing and using rights to execute implemented in the form of software decryption keys, but which prevent the user from obtaining access to any software decryption key. It is another object of the present invention to provide such a secure coprocessor which, in the course of executing protected software, will decrypt and store that software in plain text form, but which will deny access to the user to plain text of protected software. It is another object of the invention to provide such a coprocessor notwithstanding the fact that the architecture and instruction set of the coprocessor are widely known.